Question: $ { {-1} \times \left[\begin{array}{rr}{1} & {-2} \\ {1} & {2}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-1}\times{1} & {-1}\times{-2} \\ {-1}\times{1} & {-1}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-1} & {2} \\ {-1} & {-2}\end{array}\right]}$